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Full text of "Methyl bromide fumigation of cottonseed in freight cars for the destruction of pink bollworms"

1JBKAKI 



<*TATE PLANT BOARD 

June 1952 



E-838 



United States Department of Agriculture 

Agricultural Research Administration 

Bureau of Entomology and Plant Quarantine 



METHYL BROMIDE FUMIGATION OF COTTONSEED IN FREIGHT CARS 
FOR THE DESTRUCTION OF PINK BOLLWORMS^ 

By G. L. Phillips, 
Division of Stored Product Insect Investigations 



From 1945 to 1951 experiments were carried on in Texas to determine 
how methyl bromide fumigation could be utilized in the treatment of cotton- 
seed originating in areas quarantined because of the pink bollworm, to 
prevent it from being disseminated through transportation. Heat treat- 
ment had long been the standard practice, but in many instances fumiga- 
tion would be much easier. 

Preliminary tests demonstrated that pink bollworm larvae embedded 
in cottonseed were killed by exposure to moderate concentrations of 
methyl bromide. In 1946 methyl bromide fumigation of sacked cotton- 
seed intended for planting purposes was approved for use under the pink 
bollworm quarantine (BEPQ 558). In a revision of this quarantine in 1948 
methyl bromide fumigation of bulk cottonseed in large steel storage tanks 
was approved for use. A forced circulation system was provided to 
distribute the gas through the seed mass (Phillips and Bodenstein 1). 
The development of a method for fumigating bulk cottonseed in freight 
cars or trailer vans is described herein. 

Tests on freight-car fumigation were carried on at El Paso from 
1945 to 1949. During 1949 and 1950 further tests were made near San 
Antonio. The first commercial evaluation tests were made at Lubbock. 

All tests were made with carload lots of bulk cottonseed. In the El 
Paso area no cottonseed was moved commercially by railway freight; 
so it was necessary to load freight cars especially for the tests, and 
then remove the seed before another loading. Cottonseed and unloading 



1/ The following members of the Bureau assisted: J. K. Blocker, 
A. L. Broman, J. S. Cook, Roy A. Fischer, A. H. Halverson, G. G. 
Harris, P. L. Netterville, R. R. Rost, and R. S. Van Hoak. The 
following members of the Texas Department of Agriculture also assisted: 
C. W. Foster, G. C. Harris, and Edgar Jung. Acknowledgement is 
also due to L. F. Curl, director of the Southwestern Region of the Bureau, 
for his constant support of the research program. 



facilities were kindly provided by the Farmers Cooperative Oil Mill at 
El Paso. Tests near San Antonio were performed in carloads of seed 
provided by the Swift and Company Oil Mill. 

Because of the large amount of labor needed for loading and unloading 
cars, locating samples, and cutting thousands of individual cotton seeds 
to determine mortality (samples averaged from 13 to 60 larvae per 1,000 
seeds), only a few carloads could be tested in one season. 

Tests without Forced Circulation 

Before the value of forced circulation was demonstrated by fumigation 
in steel storage tanks, various methods were used to apply methyl bromide 
in efforts to attain satisfactory distribution throughout the load of cotton- 
seed. They included (1) introduction of the entire methyl bromide dosage 
in the head space above the load; (2) injection of the entire dosage into the 
load; (3) introduction of half above the head and injection of the other half; 
and (4) application as a spray (dissolved in carbon tetrachloride) to the 
surface of the load. Innovations were tried, such as partial loads, addi- 
tional sealing of floors and doorways with gas-proof material, circulation 
of the gas above the load, providing risers (vertical tunnels) through the 
load to assist penetration of dosage applied with a blast of carbon dioxide, 
and liberation of the dosage into tunnels through the load. 

In most tests 1/2 -pound samples of infested cottonseed were placed 
at selected locations throughout the seed mass. In some tests 30 of these 
samples were used, in others 24, and in a few 15. Each sample contained 
from 1,200 to 1,500 seeds and from 25 to 100 larvae. In 1948 a procedure 
for drawing and analyzing gas samples was put into use. Thereafter both 
seed and gas samples were taken to determine distribution. 

The results are summarized in table 1. In only two tests was com- 
plete mortality attained in all samples, and repeated tests with the same 
procedure gave different results. 

At first the data were interpreted to mean that freight cars were too 
leaky to serve as good fumigation chambers. After the better methods 
of sealing cars had been developed, it became evident that faulty distri- 
bution of the gas was the reason for areas of low concentration. 



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- 6 - 



Tests with Forced Circulation 

The satisfactory distribution of methyl bromide in large steel storage 
tanks resulting from forced circulation prompted attempts to utilize 
forced circulation in freight-car fumigation. The arrangement in the 
steel tanks permitted a fairly even flow of air, or gas, through the cotton- 
seed from top to bottom, because of a reduction in pressure beneath the 
load as air was withdrawn from beneath the false floor, and an addition 
of pressure above the load as the air was returned to the head space under 
considerable velocity. Since it was not feasible to place a raised floor in 
the freight car and thus permit an even reduction over the entire floor 
area, air was removed from one portion of this area by means of ducts 
laid on the car floor. 

In the exploratory tests a blower was placed on top of the load of 
cottonseed to suck air from the floor level through perforated hose 
buried beneath the load. This arrangement gave fairly satisfactory 
distribution, for all pink bollworm larvae were killed in the 24 samples 
of cottonseed in each of the last two tests. The gas samples withdrawn 
in two successful tests, in which the load was treated with 6 and 8 pounds 
of methyl bromide per 1,000 cubic feet, showed the following concentrations, 
in ounces per 1,000 cubic feet: 



Time 


6 pounds 


8 pounds 


30 minutes 


88 -12 


116 - 7 


3 hours 


50 - 12 


68-15 


6 


33 - 13 


56 - 19 


10 


33 - iu 


40-16 


24 


17 


24- 16 



These tests show that, even though complete mortality was obtained 
in all the samples of cottonseed, there was considerable variation in gas 
ncentration at the 24 selected points. The points of low concentration 
were not associated with any position in the car, although they occurred 
more often at the floor level than in the body of the load. Further tests 
with improved circulation were therefore undertaken. 

Additional tests were made in an experimental fumigation chamber 
to determine the minimum lethal concentration. The results of these 
tests are given in table 2. 



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-8 - 

From these tests it was concluded that complete mortality of pink 
bollworm larvae could be expected if the concentration could be kept 
above 10 ounces per 1,000 cubic feet at all points in a carload of seed 
for the first 10 hours. 

A better circulation system was devised which utilized a portable 
blower operated outside the car. A 4-inch duct made of downspouting and 
perforated with 1/4-inch holes on three sides at 2 -inch intervals, but with 
the distal end closed, was laid down the center of the car floor from end 
to end before it was loaded (fig. 1). A 6 -inch side duct led from the center 
to one doorway. This doorway, opposite the loading door, was sealed off 
with a paper grain doori^ properly lapped and sealed gastight, and the side 
duct was inserted through the paper seal (fig. 2). The ducts were then 
covered by the load of seed. A portable blower (fig. 3) with a gastight 
bearing was attached by 6 -inch flexible tubing to the duct protruding through 
the paper seal (fig. 4). The discharge of the blower was returned to the 
head space above the load by another length of flexible tubing attached to 
a metal collar inserted at the top of the paper seal. A blower driven by 
a 2 -horsepower motor was used. The fumigant was applied as a gas in 
the discharge duct of the blower where it was carried to the head space 
above the load and drawn down through the seed. 

A series of six tests were made with this circulation system, with a 
dosage schedule of 6 pounds per 1,000 cubic feet for 24 hours. The blower 
was operated for only about 10 minutes after the fumigant was applied. 
The ranges of concentration obtained are shown in table 3. Even though 
the concentration at certain sampling points dropped below 10 ounces at 
ine 10 -hour period, it was far above that amount after 3 hours. The fact 
that these concentrations were above the minimum lethal amount was 
substantiated by the fact that all larvae in the cottonseed samples were 
killed. 

Table 3. --Range of concentration of methyl bromide after forced-circula- 
tion fumigation of freight carloads of cottonseed. 



Number of 


Ounces per 1,000 cubic feet after- - 


samples 


30 minutes 


3 hours 


10 hours 


24 hours 



21 


16 - 43 


14- 39 


7-21 


4-9 


22 


27- 116 


15 - 112 


8-33 


6-14 


22 


20 - 114 


18 - 116 


7-24 


6 - 11 


21 


37- 84 


16 - 35 


11-27 


9-16 


22 


53- 93 


30 - 53 


14- 27 


7-26 


21 


17- 110 


16 - 69 


8-21 


6-13 



2/ The use of the paper grain door was suggested by J. K. Blocker 
and W. F. Sennette, Division of Pink Bollworm Control. 



9 - 



Application of Treatment for Quarantine Purposes 

On the basis of these tests, fumigation of cottonseed in freight cars, 
using a forced-circulation system similar to that used in the experiment, 
was authorized for quarantine purposes in February 1950. As a safety 
factor the dosage was set at 7 pounds per 1,000 cubic feet when the bulk- 
cottonseed temperature averaged 60° F. or above. Use of the method 
was limited to certain regulated areas with very light infestation where 
adequate heat-treatment equipment was not available. By arrangement 
any commercial use was to be supervised by the writer for the first 
season, in order that improvements desirable for operation under 
practical conditions might be introduced. 

The Southland Cotton Oil Company used this method on approximately 
12,000 tons of cottonseed to be shipped by rail from Lubbock, Tex. A 
total of 306 cars were fumigated in this operation. 

The same fumigation procedure was used for all cars. Only steel 
freight cars in good condition were used, each one being inspected and 
approved. Before being loaded, the floor of each car was covered with 
sisal-kraft paper, which is gasproof, and the perforated floor duct was 
put in place. The rear doorway (opposite the loading door) was sealed 
with a paper grain door, and collars were inserted for the attachment 
of the flexible tubing leading to and from the portable blower. Wooden 
grain doors were placed in the loading door to the height of the load. 
The seed was transferred from a trackside warehouse or from trucks 
by a seed pump (fig. 5), in which the cottonseed is sucked up by a powerful 
blower and blown through ducts into the car. The top of the load was 
leveled off to give at least a 2-foot head space. 

When the loading was completed, the loading door was sealed in part 
with a paste made of asbestos cement and oil and in part with scotch 
masking tape. The flexible blower ducts were attached to the collars 
in the paper grain door. The blower, which was driven by a 5-horsepower 
gasoline engine, was started, and the dosage of methyl bromide admitted 
to the exhaust duct after being volatilized by passing through a coil 
immersed in very hot water. The blower was operated for approximately 
2 minutes after the gas was introduced and then detached. The collars 
in the paper grain door were removed and the holes quickly sealed with 
gasproof paper and masking tape. The car door was then closed and the 
fumigation allowed to proceed for 24 hours without further attention. 
The blower unit was moved to the next car to be fumigated. 

As many as 16 cars were fumigated in one day, the limiting factor 
being the speed of loading. One portable blower unit was considered 
capable of handling 20 cars per day. 



- 10 - 

The actual fumigation procedure was handled by representatives of 
the oil-mill company.—' The certification of the cottonseed was handled 
by regular inspectors of the Bureau of Entomology and Plant Quarantined 

The method developed for testing the efficiency of gas distribution in 
large steel tanks, whereby two gas samples were withdrawn from a 
selected sampling point at any time during the fumigation period, and the 
results of analysis compared with a standard curve (Phillips and Latta 2), 
was adopted as a means of observing the effectiveness of the freight-car 
fumigation at Lubbock. 

The lowest concentration of gas was found to be at a point near the 
floor about half way between the car wall and the center duct and about 
one-third the distance from the end wall to the doorway. This was 
designated as the standard sampling point. A curve was plotted based 
on the average of the concentrations present at this point in tests. 
The lowest concentration present at this position in the experimental 
cars which was associated with complete mortality in biological samples 
was considered as the maximum deviation from the average. 

A sample was withdrawn from a car under fumigation by inserting 
a sampling probe through the paper grain door near the floor level along 
a line between the center of the doorway and one of the opposite corners. 
By inserting the probe 14-1/2 feet at this angle the standard sampling 
point was reached consistently with accuracy. The analysis of this 
sample was matched against the curve to indicate the efficiency of 
distribution in each car sampled. 

It was not possible to sample all cars fumigated, but an attempt was 
made to sample at least half of those fumigated each day. Analyses 
were made on samples from 162 of the 306 cars fumigated, and only 
one fell below the maximum allowable deviation. This car was re- 
fumigated. 

The samples were withdrawn when convenient, so that the time of 
sampling ranged from 30 minutes to 17 hours after the start of the 
exposure. These concentrations at the sampling points were grouped 
according to 1-hour intervals, i.e., those between 0.5 and 1.4 hours, 
1.5 and 2.4 hours, etc., and an average was taken for each interval. 
These data were compared with the concentrations found in the seed 
mass in large steel tanks under fumigation and with the concentration 
found at the standard sampling point in the experimental fumigations 
as shown in figure 6. 



3/ J. R. Richardson and Frank P. Dickson. 

4/ Certification was supervised by H. L. Alford, M. E. Currie, and 
G. W. Chowns, and performed by Inspectors T. P. Patterson, R.J. 
Morits, E. L. Wilde, E. I. Fosmire, R. K. Robinson, A. S. Pela, and 
Ike Laird of the Division of Pink Bollworm Control. They also assisted 
the research staff in many ways as their duties permitted. 



- 11 - 

The fumigation of 306 carloads of cottonseed with only one rejection 
and the satisfactory concentration patterns found in the sampled cars 
were considered ample proof of the practicability of freight-car fumiga- 
tion with the apparatus developed for forced circulation. Therefore, in 
July 1950, the quarantine regulations in BEPQ 558 were further modified 
to authorize freight-car fumigation in lieu of heat treatment in all lightly 
infested areas in Texas, New Mexico, and Oklahoma, and as an additional 
treatment for cottonseed moving from heavily infested areas. 

Summary 

Methyl bromide fumigation was authorized for the treatment of sacked 
cottonseed in 1946, and for bulk cottonseed in large steel storage tanks 
fitted with means for forced circulation in 1948. A method for fumigating 
bulk cottonseed in freight cars, developed between 1945 and 1951, is 
described in this paper. 

Efforts were made to attain a satisfactory distribution of methyl 
bromide throughout a freight-car load of cottonseed by various methods 
of application, such as applying it in the head space above the load, 
injecting it into the load, applying half the dosage above and injecting 
half, and dissolving in carbon tetrachloride and spraying on the surface. 
None were successful. Other innovations, such as partial loads, additional 
sealing of floors and doorways with gas proof material, providing risers 
(vertical and horizontal tunnels) through the load to assist in penetration, 
and following the application with a blast of carbon dioxide, were also 
unsuccessful. 

Attempts were then made to adapt the method of forced circulation 
used in fumigation of cottonseed in large steel storage tanks. A gas- 
distribution pattern was obtained that provided a lethal concentration at 
all sampling points. In the method finally adopted a portable blower 
operated outside the freight car pulls air from beneath the load through 
a specially designed duct system and returns it to the space above the 
load. The blower is run during gas volatilization and for 2 to 10 minutes 
thereafter, then disconnected, the car sealed, and the blower moved to 
the next car to be fumigated. 

This method for treating cottonseed was authorized for use on quar- 
antined cottonseed in February 1950 in a limited area under supervision. 
The dosage schedule is 7 pounds per 1,000 cubic feet for 24 hours expo- 
sure at 60° F. or above, and 8 pounds at lower temperatures. 

The first trial on a commercial basis was at Lubbock, Tex., where 
approximately 12,000 tons of cottonseed in 306 freight cars were 
fumigated. All but one of the 162 cars that were checked by gas analyses 
were found to have the required gas concentration. 

In July 1950 the forced-circulation method was authorized as an 
alternate method for treating cottonseed for the destruction of pink boll- 
worm larvae. 



-12- 



Literature Cited 

(1) Phillips, G. L., and W. G. Bodenstein 

1948. A successful large-scale experiment in methyl bromide 

fumigation of bulk cottonseed for pink bollworm control. 
Jour. Econ. Ent. 41: 804-805. 

(2) Phillips, G. L., and Randall Latta 

1949. Current use of methyl bromide for the fumigation of cotton- 

seed. Down to Earth (Dow Chemical Co.) 5(1): 11-13. 



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Figure 2. --Car loaded ready for fumigation, 
showing collars inserted at top and bottom 
of grain door. 




Figure 3. --Gasoline engine mounted to drive 
circulating blower. The volatilizer unit and 
the scales for weighing dosage are also 
shown. 



- 15 




Figure 4. --Volatilizer and circulating unit 
attached to one of several loaded cars ready 
for fumigation. The unit could handle one 
car in 15 to 18 minutes. 




Figure 5. --Portable seed blower transferring 
cottonseed from a truck to a freight car. 



- 16 



UNIVERSITY OF FLORIDA 

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Commercial freight-car fumigations 




Experimental freight-car fumigations 



Steel-tank fumigations 



8 12 16 

TIME-HOURS 



20 



24 



Figure 6. --Methyl bromide concentrations at standard sampling points in com- 
mercial and experimental freight-car fumigations as compared with steel- 
tank fumigations.